Convert curve to particle hair guide
There are two free add-ons for Blender that can convert curves and sheets (hair cards) to hair particles guides:

HairNet 0.6.3 (https://github.com/Jandals/HairNet/releases) forum thread at blenderartists.org
Particle Hair Guides (https://github.com/Lichtso/hair_guides) forum thread at blenderartists.org

The add-on Select Islands by Face Count by Stan_Pancakes is a useful helper if you want to convert hair cards to particles with one of the add-ons above.